Various publications describe the uses of and methods of using catalysts or other additives during a solid state polymerization process of condensation polymers.
In these polymerization processes, it has been customary to introduce the catalyst species into the melt phase of the polymerization process followed by solidification and, optionally, crystallization. Thus, when said catalyst treated polymer is subjected to solid state polymerization, the catalyst is available to exert its catalytic action. Catalyst remains in the finished, solid state polymerized product and all end use polymer products contain measurable quantities of the catalytic species. In any subsequent use, where the catalyst-containing polymer is exposed to heat, a molecular weight increasing condensation reaction may start to occur because the catalyst is still present.
The present invention adds the catalyst or other treatment agent as a gas or dissolved in a liquid, which improves the contact of the polymer, typically in the form of a particle or a pastille, with the catalyst or treatment material and, if the agent is sufficiently volatile, also facilitates removal of the agent from the system. The agent is then removed easily from the system after contact with the polymer by the inert gas sweep employed in solid state polymerization processes and the resulting polymerization product is substantially free of catalyst or treatment agent.